Numerous sites across the country are impacted with light, nonaqueous-phase liquids (LNAPLs). LNAPL recovery is often a default or presumptive remedial objective in most regulatory programs. Unfortunately, LNAPLs have historically posed a significant challenge to site remediation for various reasons. A variety of passive and active remedial technologies exist that have applicability to different LNAPL and site conditions. This document provides a technical overview of natural source zone depletion (NSZD) for LNAPLs, which, when appropriately evaluated, can serve as an objective benchmark by which to compare the relative effectiveness of different remedial alternatives.